It must be a floating point error.
I would hazard one of the following:
&lat=-40.99999999&lon=-57
&lat=-41&lon=-56.99999999
&lat=-40.99999999&lon=-56.99999999
The first one should be it, since -57 is correct floating point-wise when it came up as a moon coordinate previously. -41 has never been the coordinate, so I suspect it should actually be -40.99999999
Much less luck this time.
I've got a most likely spot at -41, -57. No other options available, but there are a three moon options connected.
I've tried
0,29 - 50%
-58,-94 - 80%
-83,-146 - 65%